Blood pressure is a major input into the risk equations for heart attacks, strokes, kidney disease, and so on. For the most part we've used a one-time measurement, assuming it's an average. But if we had a time-series of blood pressure, I could see blood pressure variability actually becoming an important metric.
I agree with you and understand completely. It just seems more an "as-needed" item that'd be "prescribed" by a medical professional rather than a consumer-facing gadget.